Synthetic coating compositions



Patented a, 12, 1937 com positions for finishing various types of, surface,

and hasparticular reference to a new and novel 6 tionof'ilirfuryl alcohoL'alone or in admixture with furiuraldehyde, and a dehydrating agent such as sulfuricacid. More particularly, it refers to a coating composition comprising a partially reacted furfuryl alcohol, dehydrating agent resinand amutual solvent which inhibits further interaction of the resin-forming constituents so that the mixture may be safely stored; a i

It is well known that furfuryl alcohol alone,

or inadmixturewith furfuraldehyde, canbe rel5 acted with dehydrating agents to form resinous condensation products. It is believed that the resiniflcation occurs by the splitting off of water and resultant condensation into a condensed aldehyde, which recondenses until a molecule of 20 resin-forming proportion is formed. The reaction occurs most rapidly at elevated temperatures,

becomes insolubleandprecipitates. I

Because the final resin is substantially i'nsoluble in practicallyall of the common solvents, and

U 3 because the resinis extremely resistantto strong 30 acids, we have felt that it would make an exceptional coating material for special purposes; but the fact that it could not be handled as a coating solution preventedits use.

Attempts were made to obtain the desired re- 85 action by spraying thedehydrating agent over a surface coated with the alcohol or alcohol alde-' I v yde mixture. This method was abandoned because of the difliculty of keeping the first coating on the work, and the necessity for heating the :4 coating if speed of resiniflcation were to be ob- ,tainedi Mixture of the two materials directly before application was also attempted, but similarlypoor results were obtained, and the added complication of {relation o! the mixture on overnight standing made this method much more undesirable even than the first method;

We have discovered that if the ingredients be reacted partially, to a stage where the reaction 0 mass is still soluble, and the mass is then disi solved in a suitable solvent, that a satisfactory coating vehicleis obtained, This may be mixed before use with more dehydrating agent to obtain t complete reaction, but the reaction is far enough 1 alongso that the coating has suflicient viscositysolvents.

land dhesion to adher e properly to thework, and

no heat is needed to obtain the final desiredinsoluble stageina reasonabletime. 1 w; i Sulfuric acid is preferredndehydrating agent, because of its miscibility'with many of the common organic solvents in which the resin may be dissolved.

In a preferred form of our invention, we made a preparatory solutionof concentrated acid (66 Bauml in diacetone alcohol, using 4 liquid ounces of acid to 1 gallon of solvent. We then mixed Ounces Above solution Furfuryl alcohol ,16 Furfuraldehyde 16' and heated the mixture to240" Fsfor an hour. "l'he batch was allowed to cool, and was reduced with Ounces Cellosolve (ethylene: slycol monoethyl ether) 6 Methyl isobutyl ketone 6 mixing; the mixture had, however, gelled by the morning of the third day. The resultant film was unaffected by petroleum and coal tar naphthas,

and by the ordinary ester and ketone lacquer Its resistance to acids was unusually good; it required more than 20 minutes for concentrated sulfuric acid to break through the film.

Fu -fury] alonhnl allons 2% Fln'furaldehyde do 5% Acid solution ..liquid ounces 9%.

were heated to 230-241? F. for about 90 minutes. There was then added, as a gelation inhibitor 15 liquid ounces tricresyl phosphate, and the resin was then dissolved in 4 gallons solvent naphtha. A separate solution was made by dissolving 2% poundslOO second R. S. nitrocellulose (30% alcohol) in3% gallons of amyl acetate and F94 gallon of. Cellosolve, and the two solutionswere mixed. The mixture was also very stable in the can (six monthswithout signs of gelation); and on blending 8 parts of it with 1 part of the above acid solution, a. coating material was obtained which could be sprayed for at least 24 hours after blending. This coating, in spite of its content of nitrocellulose, was as unafiected by nitrocellulose solvents as the first example; its acid resistance was somewhat improved.

Other dehydrating agents may be'used to replace the sulfuric acid, although results are not quite as good. Among these agents which cause the condensation are zinc chloride, phosphorus pentoxide, and chromic acid.

It is important that the solvent include a percentage of some solvent which is a retarder or inhibitor of further condensation, in order to in-' hibit gelation in the can. Alcohols, esters, ketones, ethers and the aromatic hydrocarbons are satisfactory inhibitors, as .are the common ester plasticizers such as dibutyl phthalate and tricresyl phosphate. however, are not satisfactory gelation inhibitors, and the use of large percentages of these solvents produces rapid gelation. The use of substantial percentages of the inhibiting solvents permits the carrying of the resin to a higher degree of condensation than if less solvent is used.

The aliphatic hydrocarbons,

The partial resins can be used as coating compositions, but they do not then possess the desirable properties of substantial insolubility and resistance to acid, which are the desirable properties oi the resin after reaction to insolubility.

We claim:

1. The method of producing a highly acid and solvent resistant coating on an object which comprises reacting a material of the class consisting of Iurfuryl alcohol and a mixture of furfural and furiuryl alcohol with a promoter for resinification to obtain a soluble resinous preliminary condensation product, dissolving the soluble resin in a solvent which retards further reaction, whereby a stable composition is obtained, adding to this composition just before use a further portion. of promoter and applying the mixture to the surface whereby the reaction to the insoluble stage is completed on the object.

2. The method of claim 1 in which the resinification promoter is sulfuric acid.

ALBERT J. HEBERER. WM. R. MARSHALL. 

